Recovery of nitrogen bases



Fbb.13,1951 c.H.o.BERG

RECOVERY OF NITROGEN BASES Filed July 9, 1945 WOHZMH jf Patented Feb. 13, 1951' 2,541,458 RECOVERY OF NITROGEN BASES Clyde H. O. Berg, Long Beach, Calif., assigner to Union Oil. Company of California, Los Angeles, Calif., a corporation of California Application July 9, 1945, Serial No. 603,849V 14 claims. (c1. 26o- 290) This invention relates to the recovery of nitrogen containing compounds from hydrocarbon fractions in which they are contained such as may be obtained from shale oil, shale oil distillates, tar sand, or petroleum fractions.

It is well known that there is present in petroleum, oil shales. and tar sands and in distillates thereof a. small percentage of organic nitrogen compounds particularly in oils of naphthenic origin such. as those found predominantly in Californiafields. Many of these nitro-gen compounds show basic characteristics in that they are reactive with dilute acids and consequently unsaturation of the nitrogen compound or the like. Thus in a simple example, if pyridine is hydrogenated a simplel amine isv formed exhibiting. stronger basic properties than does the pyridine itself. No definite; criteriav can be established as yet whereby thenature of these various nitrogen bases can be. accurately predicated. However, such prediction is, not necessary according to the, present. invention inasmuch as I am able to effectively separate any of' these nitrogen bases from the hydrocarbon fractions containing them.

Methods of separation ofi nitrogen bases from hydrocarbons have been known in the art for some time. These methods include such proce. esses as. extraction. of the hydrocarbon oil containing the nitrogen bases withsulfuric acid. followed by neutralization off the extract with caustic soda whereupon the nitrogen bases are thrown out as an immiscible layer. Other methods involve the usage of variousV metal salts to form complex saltsr with the nitrogen base. as for example `('Base)2.Zn C12 asy obtained by contacting the nitrogen bases with zinc' chloride. method asv described by Mahan and Baileyv (J. A. C. S`. 59, 449, 1937)v further involves the decomposition of the double salt at elevated tempera-.- tures. Still othersv involve the usage. of comE This l paratively weak acids. such as those having dis-- sociation constants in aqueous. solutions inthe order from about 10-3 tov about lOv-S. under conditions to form two fluid phases, at least one of which is liquid and comprises a fatty aqueous. solution containing the: acid and adsorbed nitrof gen base, and the other which is liquid or vae' porous and: consists essentially of the organic: substance from which at least a portion. ofY the nitrogen bases have.been.removed..

The two phases are separated and the fatty acid solution is then stripped' with steam orv other' hot convectionY medium to remove the nitrogen bases therefrom.

One of the more important disadvantages ofv these older methods of recovery is: that. only arelatively small portion of` the nitrogen. bases is recovered from the oil due possibly to the fact that these bases vary widely in their basic char.- acteristics as above. described.

lt is an object of the presentinvention to provide an improved process for the: recovery of nitrogen bases from various hydrocarbon frac.- tions in which they are contained, this process` being independent, with the exception. cf minorsult in improved recovery of nitrogen bases andvv which may be readily recovered from the nitrogen base extract and reused in the process.

Other objects and advantages of my invention will become-apparent to. those slgilled in the art as the description thereof proceeds.

In its essentials my process comprises treating petroleum or a fraction thereof containing one or more nitrogen bases with a volatile acid or a nonvolatile acid salt together with a mutual' solvent for the acid and hydrocarbon to effect the improved recovery of the nitrogen base. It hasl been postulated that one reason for the comparatively inemcient separation of nitrogen bases from hydroc'arbons` is because ofthe poor solubilityl ef the re-f agents normally employed in the extraction. Iv

have found that this difficulty may be overcome by combiningY with the extractiva solvent" a rnuzzl tual solvent which has the effect of increasing the solubility of the extractive solvent in the= hydrocarbon resultinginimproved recovery of the nitrogen bases. g.

annua As extractive solvents for this process I prefer to employ the volatile acids such as hydrochloric, formic, acetic, propionic, carbonio, sulfurous and the like. Generally included in the category of volatile acids according to the present invention are those acids which may be vaporized at a temperature below about 200 C. and preferably below about 150 C. In this regard hydrocarbon fractions containing nitrogen bases of strongly basic character will require the usage of the weaker of the above acids such as acetic, carbonio, or sulfurous acids. Those fractions containing very weak nitrogen bases whose acid salts will readily decompose on heating will'permit they usage of the stronger Volatile acids such as hydrochloric acid and formic acid, and the like.

Whereas the above volatile acids may be employed in the recovery of lower boiling nitrogen bases such as those boiling below the particular volatile acid employed we have found that from an operational standpoint it is preferable to modify the process and employ an aqueous solution of a non-volatile acid salt, in conjunction with the mutual solvents hereinafter disclosed, such as sodium dihydrogen phosphate, sodium monohydrogen sulfate and the like, which aqueous salt solutions permit the more ready recovery of the nitrogen bases from the extract. These non-volatile acid salts are inorganic salts having a replaceable acid hydrogen.

As mutual solvents for the process according to my invention I may employ any solvent in which both the extractive solvent and the hydrocarbon fraction are at least partially soluble and I prefer to employ those solvents which, like vthe volatile acid, boil below about 200" C. and

preferably below about 150 C. Such solvents include for example the low boiling alcohols and ketones such as methyl alcohol, ethyl alcohol, isopropyl alcohol, acetone, methyl ethyl ketone and the like. The mentioned alcohols are all monohydric alcohols. Of these I have found methanol to be the most effective in improving the recovery of the nitrogen bases. Briefly the process according to my invention comprises a continuous countercurrent extraction of the hydrocarbon fraction with the mutual solvent and the extractive solvent together with water washing at the top of the extraction tower to avoid loss of solvent or the contamination of the hydrocarbon raffinate. This process and the modifications thereof which may be employed depending upon the nature of the nitrogen bases to be recovered may be more readily understood by reference to the accompanying process diagram.

l In the drawing equipment and piping are shown to permit two types of operation depending upon the usage of a volatile acid or an aqueous solution of a non-volatile acid salt as the extractive solvent. If a volatile acid is to be employed as the extractive solvent a hydrocarbon feed containing the nitrogen bases is withdrawn from tank I by means of line II controlled by valve I2 and is pumped by pump I3 via line I4 into the bottom of extraction column I6. The volatile acid and the mutual solvent are introduced into extraction column I6 by means of line I1 entering column I6 at some point intermediate between the point of feed inlet and ranate outlet. The volatile acid and mutual solvent entering extraction column I6 by means of line I1 has the effect or" extracting the nitrogen bases from the hydrocarbon fraction. the latter passing 4 upwardly in the column and the nitrogen basessolvent solution passes downwardly therein.

Water is introduced at a point above that of solvent introduction as for example by means of line I8 which has the eiect of water washing the ascending hydrocarbon raffinate to remove residual amounts of the extractive solvent and the mutual solvent from the hydrocarbon. The water progresses downwardly in the column and isbwithdrawn together with the solvent-nitrogen base phase as hereinafter described. The hydrocarbon raffinate is withdrawn from the top of extraction column I6 by means of line I9 controlled by valve 2E! and is pumped by pump 2| via line 22 into the hydrocarbon rafnate storage tank 24.

The lower phase in extraction column I6 comprising the volatile acid, the mutual solvent, nitrogen bases, and excess water employed in washing the raffinate is withdrawn from the bottom of the column by means of line 25, controlled by valve 26 and is'pumped by pump 21 Via line 28 into stripping column 30. In stripping column 30 the acid, solvent and water are stripped from the nitrogen bases and are taken overhead by means of line 3l controlled by valve 32 passing into condenser 33. From condenser 33 the overhead passes into reflux drum 34 from which it is withdrawn by means of line 35 and is pumped by pump 36 into line 31 controlled by valves 38, 39 and 40. A part of the condensate may be returned to stripping column 30 by means of line 4I to serve as reflux in the stripping or fractionating operation. The remainder of the condensate passes through valve 38 via line 42 into fractionating column 44.

Returning to stripping column 30 the nitrogen bases remaining as bottoms in the operation are withdrawn from the bottom of the column by means of line 45 controlled by valve 46 and are passed into line 41 controlled-by valves 48 and 49. In the 'presently described method of operation these nitrogen bases'pass through valve 48 and line 50 and are pumped by pump 5I via line 52 into the nitrogen base'storage tank 54.

In fractionating column 44 the acid and mutual solvent are distilled overheadleaving the excess water as bottoms in the distillation. The overhead comprising the acid and mutual solvent is withdrawn from fractionating column 44 by means of line 55 controlled by valve 56 and. is passed into condenser 51. From condenser 51 the condensate is passed'into reux drum 58 and from thence'into line 59 and is pumped by pump 60 into line 6I controlled by valves 62 and 63 and part of the condensate is returned to fractionating column 44 by means of valve 62 and line 64 to serve as reux in the distillation. The remaining portion of the condensate passes through valve 63 and through line I1 back, to extraction column I6 to be reused in the extraction.

The bottoms from fractionating column 44 comprising substantially solvent-free water is withdrawn by means of line 65 controlled by valve 66 and is pumped by pump 61 via line I 8 back to extraction column I6 to be reused as hereinbefore described.

The operation as described need be modified only slightly for the extraction of hydrocarbon fractions containing nitrogen bases boiling below the volatile acid extractive solvent and the mutual solvent. If such be the case the overhead from stripping column 30- will consist essentially of. the nitrogen bases and will be passed directly therefromto the nitrogen basefstoragetank.. The bottoms from stripping column will consist in. this case of the volatile acid, mutual solvent and water and will be passed directly to the fractionating column 44 to be resolved. into an acid-mutual solvent fraction and a Water fraction as described above.

If, however, it is desired to extract` a low boiling nitrogenbase from a hydrocarbon fractionit may bev preferable to employ an aqueous solution of a non-volatile acid salt. as hereinbefore described as the. extractive solvent. If. this be the case, hydrocarbon feed containing the.- low boiling nitrogenv base will 'be withdrawn from. tank I0 by means of line II, controlled by valve I2 and pumped by pump I3v via line I4 into the extraction column I5 as before. The difference4 in the operation resides largely in the point of introduction of the. various constituents into. extraction column I3. If a volatile acid is employed it.` is. introduced into. the column together with the. mutual solvent by means of line Il, but if an aqueous solution of a non-volatile acid salt is employed it is introduced at the top of the eX- traction column by means of line I3 and the mutual solvent is introduced as before by means of line I'I'. In this manner the mutualv solvent has the effect of solubilzing the extractiva solvent in the hydrocarbon below the point of introduction at line I. The extractive solvent entering by means of line I3 and being in the form of an aqueous solution has the same: effect as: the introduction of water by means of. line* I8 as described in the above process; namely, that of extracting any residual mutual solvent remaining in the hydrocarbon raffinate..

The. extractive solvent, mutual solvent, and.l water are withdrawn from the bottom of the column I6 by means of line 25 controlled by valve 2,6. and are pumped by pump 2'I via line 23 into the stripping column 38. The hydrocarbon raffinate. is withdrawn as above from extraction column I 6 by means ofline I9 controlled by valve 2U, is. pumpedr by pump 2l via line 22 into the hydrocarbon raffinate storage tank 24.

In the stripping column 3i! the volatile nitrogen bases together with the mutualk solvent,l and in most cases water, are distilled overhead andv are. withdrawn from thev column by means of line. 3l controlled by valve. 32 passing therefrom into condenser 33. The condensate collecting in re;-l flux` drum 3.4v after condensing in condenserl 33. is. withdrawnv from the reflux drum by means of line` and is pumped by pump 36 into line 31 controlled'. byv valves 38, 39 and 40 and a part. thereofl is passed through valve 40 via line 4I baick. to' column 30 to serve as' reux in the distillation. The. remainder of the condensate is` passed` through valve 39 via line 'I0 into the; separator '12 wherein a phase separation occurs` between the water and mutual solvent in one case and the nitrogen bases in the other.

The nitrogen base phase is withdrawn from the top of separator'IZ by means of line 'I3 controlled by valve 14, is passed through line and is pumped by pump 5.! via line 52 into the nitro.- gen base storage tank 54'.

The lower phase in separator 'I2 comprising mutual solvent and water is withdrawn therefrom by means of line 15, controlled by valve 'I6 and is passed via line 42 into fractionating column 4'4.

vIn fractionating column 44 the mutual solvent and' water are separated' by simple distillation; the solvent passing overhead byy means. of'line 55' 6. controlled by valve 516 into, condenser 5.1 rand subsequently into reflux. drum. 58'. The'. con.- densed mutual. solvent isv withdrawn from reflux drum 5d byl means of line 59,. is. pumpedy by pump .K

60 into: line 6I controlled by'valves: 32. and 63. and apart thereof is returned via line 64 to fraction.- atlng column 44 to serve as reflux in the distillation. The remaining condensate is passed through valve4 53 via line I'I back to the extraction column I6. The bottoms from the distillationv in column 44 comprising substantially solvent-free water is withdrawn therefrom by means of line 65, controlled by valve 33 and.. is pumped by pump B'I through line I8 back to the extraction column I6.

Returning to stripping column 3Il wherein the separation of water nitrogen bases and mutual solvent from the non-volatile acidsalt solution was accomplished,. the non-volatile acid salt solution is Withdrawn from thebottom of. the column by means of line.l 45, controlled. byl valve 46 passing into linev 4-1 controlled by valves 48 and 49. This aqueous solution of the non-vola.- tile acidi salts is passed through valve 49 and line; 68 and is pumped by pump 59: into` line Itv where.- in it is commingled with any water which may have been distilled therefrom in stripping column 30- and Which is recovered in fractionatingy col.- umn 44 and returned via. line I8 to recombine with the salty solution.

It is apparent from the above description of my process that it exhibits a wide flexibility of. methods of. operation,A ofi extractive solvents which may be employed,4 of mutual solvents which may be employed and, of nitrogen base containing hydrocarbon fractions which may be treated. The essential element of my invention asis apparent to one skilled in the art comprises the use of a mutual solvent to increase the solubility of the extractive solvent, whether it be a volatile acid or a non-volatile acid salt, in the hydrocarbon fraction in order to obtain improved recoveries of nitrogen bases from these hydrocarbon. fractions. This. is the essential element of my invention and I do not wish to be .limited on the grounds of the foregoing description to any particular modification in the operation or to any particular extractive solvent or mutual solvent.

I have, however, found certain compounds which appear to be effective as extractive solvents and certain compounds which appear to be effective as mutual solvents. As extractive solventsv I have found that the volatile acids such as hydrochloric acid, formic acid, acetic acid, propionic acid, carbonio acid and sulfurous acid are satisfactory for the operation. In the use of these acids it is necessary to use a certain amount of discretion in the choice of the particular acid to be employed dependent upon the characteristics of the nitrogen base or bases to be recovered. If. these, nitrogen bases are of strongly basic nature itis advisable to employ one of the weaker of the above acids inasmuch as a strong acid such. as hydrochloric acid will result in the formation of a dihcultly decomposable salt whereas such will'I not' be the case ifY a weak acid is employed. Further, asv extractive solvents, particularly as extractive solvents for the recovery of the low boiling nitrogen bases such as for example thosev which boil below about 106 C. I have found thatv aqueousA solutions of various non-volatile acid salts such as sodium` dihyd'rcgen sulfate, sodium` monohydrogen phosphateand' the like are satis-- factory;

Y 7 .As mutual solvents I have found .that any compound or mixture of compounds capable of increasing the solubility of the extractive solvent in the hydrocarbon may be employed. This definition covers a wide range of compounds but I have found that the alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, and the like, and particularly methanol are the preferred compounds to be employed as mutual solvents.

The foregoing description of the elements and various processes of my invention is not meant to be limited in any way inasmuch as many modifications thereof will occur to those skilled in the art Without departing from the spirit or scope of my invention and of the following claims:

1. A process of recovering nitrogen bases of a plurality of types from hydrocarbon fractions containing the same which comprises extracting the hydrocarbon fraction with an extractive solvent comprising an aqueous solution of a compound selected from the class of compounds consisting of the volatile acids boiling below about 200 C. and the non-volatile acid salts having a replaceable hydrogen and a mutual solvent for said extractive solvent and hydrocarbons comprising a compound selected from the class of compounds consisting of the low molecular weight monohydric alcohols and ketones to remove the nitrogen bases substantially completely from said hydrocarbon fraction, water washing the extracted hydrocarbon raffinate, combining the resulting wash water with the extract phase, separating the nitrogen bases from the extract and reusing the Water, selective solvent and mutual solvent in the extraction.

2. A process of recovering nitrogen bases of a plurality or types from hydrocarbon fractions containing the same which comprises extracting a hydrocarbon fraction with an extractive solvent comprising an aqueous solution of a volatile acid boiling below about 200 C. and a mutual solvent for said extractive solvent and hydrocarbons comprising a compound selected from the class of compounds consisting of the low molecular Weight monohydric alcohols and ketones to remove the nitrogen bases substantially completely from said hydrocarbon fraction, water washing the extracted hydrocarbon fraction combining the resulting wash water with the extract phase, separating the nitrogen bases from the extract phase, separating the volatile acid and mutual solvent from the excess water in the extract phase and reusing the volatile acid, mutual solvent and water in the extraction.

3. A process of recovering nitrogen bases of a plurality of types from hydrocarbon fractions containing the same which comprises extracting a hydrocarbon vfraction with an extractive solvent comprising an aqueous solution of a nonextract phase, separating the nitrogen bases fromsaid mutual solvent and reusing said mutual solvent and said extractive solvent in the extraction.

4. A process according to claim 2 wherein the volatile acid is selected from the class of acids consisting of hydrochloric acid, formic acid, acetic acid, propionic acid, carbonio acid and sulfurous acid. 5. A process according to claim 3 wherein the acid salt is selected from the class of compounds consisting of sodium dihydrogen phosphate and sodium monohydrogen sulfate.

6. A process according to claim 2 wherein the mutual solvent is methanol.

7. A process according to claim 3 wherein th mutual solvent is methanol.

8. A process of recovering nitrogen bases of a plurality of types from hydrocarbon fractions containing the same which comprises extracting the hydrocarbon fraction with an aqueous solution of hydrogen chloride and methanol to remove the nitrogen bases substantially completely from said hydrocarbon fraction, water washing the extracted hydrocarbon raflinate, combining the wash water with the acid-methanol-nitrogen base extract, distilling the water, methanol and acid from the nitrogen bases extracted from the hydrocarbon fraction and separating the excess water from the acid and methanol, returning the latter to the extraction step and the water to the water washing step.

9. A process of recovering nitrogen bases of a plurality of types from hydrocarbon fractions containing the same which comprises extracting the hydrocarbon fraction with acetic acid and methanol to remove the nitrogen bases substantially completely from said hydrocarbon fraction water washing the extracted hydrocarbon railinate, combining the wash water with the acidmethanol-nitrogen base extract, distilling the water, methanol and acid from the nitrogen bases extracted from the hydrocarbon fraction and separating the excess water from the acid and methanol, returning the latter to the extraction step and the Water to the water washing step.

10. A process of recovering nitrogen bases of a plurality of types` boiling below about 200 F. from hydrocarbon fractions containing the same which comprises extracting the hydrocarbon fraction with an aqueous solution of a non-volatile acid salt having a replaceable hydrogen and a mutual solvent for said aqueous solution of a non-volatile acid salt and hydrocarbons comprising a compound selected from the class of compounds consisting of the low molecular weight monohydric alcohols and ketones, to remove the nitrogen bases substantially completely from said hydrocarbon fraction washing the extracted hydrocarbcn raffinate with fresh extractive solvent, adding the extractive solvent from said washing to the extraction step, separating the extract phase from the rainate phase, separating the nitrogen bases and mutual solvent from the aqueous solution of the non-volatile acid salt and excess water in the extract phase, separating said nitrogen bases from said mutual solvent by simple phase separation, returning said solvent to the extraction step and said aqueous non-volatile acid salt together with the excess water to the water washing step of the process.

11. A process of recovering nitrogen bases of a plurality of types from hydrocarbon fractions containing the same which comprises extracting the hydrocarbon fraction with acetic acid and methanol to remove the nitrogen bases substantially completely from said hydrocarbon fraction,

Water washing the extracted hydrocarbon fraction, combining the resulting Wash water with the extract phase, separating the nitrogen bases from the extract phase, separating acetic acid and methanol from the excess water in the extract phase and reusing the acetic acid and methanol in the extraction.

12. A process according to claim 3 wherein the acid salt is sodium monohydrogen sulfate and the mutual solvent is methanol.

13. A process according to claim 2 wherein the Volatile acid is sulfurous acid and the mutual solvent is methanol.

14. A process according to claim 2 in which the l0 volatile acid is hydrochloric acid and the mutual solvent iis acetone.

. CLYDE H. O. BERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 10 Number Name Date 2,035,102 Straford Mar. 24, 1936 2,035,583 Bailey Mar. 31, 1936 2,085,545 Retalliau June 29, 1937 2,199,930 Walsko May 7, 1941 15 2,309,324 McAllister Jan. 26, 1943 

1. A PROCESS OF RECOVERING NITROGEN BASES OF A PLURALITY OF TYPES FROM HYDROGEN FRACTIONS CONTAINING THE SAME WHICH COMPRISES EXTRACTING THE HYDROCARBON FRACTION WITH AN EXTRACTIVE SOLVENT COMPRISING AN AQUEOUS SOLUTION OF A COMPOUND SELECTED FROM THE CLASS OF COMPOUNDS CONSISTING OF THE VOLATILE ACIDS BOILING BELOW ABOUT 200* C. AND THE NON-VOLATILE ACID SALTS HAVING A REPLACEABLE HYDROGEN AND A MUTUAL SOLVENT FOR SAID EXTRACTIVE SOLVENT AND HYDROCARBONS COMPRISING A COMPOUND SELECTED FROM THE CLASS OF COMPOUNDS CONSISTING OF THE LOW MOLECULAR WEIGHT MONOHYDRIC ALCOHOLS AND KETONES TO REMOVE THE NITROGEN BASES SUBSTANTIALLY COMPLETELY FROM SAID HYDROCARBON FRACTION, WATER WASHING THE EXTRACTED HYDROCARBON RAFFINATE, COMBINING THE RESULTING WASH WATER WITH THE EXTRACT PHASE, SEPARATING THE NITROGEN BASES FROM THE EXTRA AND REUSING THE WATER, SELECTIVE SOLVENT AND MUTUAL SOLVENT IN THE EXTRACTION. 